1. Field of the Invention
The invention relates to power supplies and, more particularly, to a power supply system and control method for a power supply system having at least two power sections.
2. Description of the Related Art
In order to supply a predefined voltage to a load, use is often made of a power supply device that converts the electrical energy of a supply network into the desired voltage. This is usually a switched-mode power supply comprising a power section and a control unit. Devices comprising a plurality of power sections, these being actuated by dedicated control units in each case, are also used.
A power section comprises power components that are designed for a specific nominal load. This nominal load is usually derived from the permissible thermal loading of the component. If a connected load requires a higher power, use is made of power supply systems having power section outputs that are connected in parallel. In this way, structurally identical power sections can be used for different output powers. This simplifies the storage thereof, and allows higher unit volumes with correspondingly reduced manufacturing costs per unit.
If a plurality of power sections is connected in parallel, provision should be made for all of the power sections to participate in supplying the load, in order to ensure an even loading. This applies in particular to power supplies comprising electronic fuses that have a current limit up to which the power supply is operated in a normal mode. In the absence of a balanced load distribution when using such power supplies, one power section will switch into a safety mode before a parallel-connected power section reaches its full working capacity. This state usually results in disconnection of the power supply system, because the safety mode is only maintained for a specific time before disconnection is necessary due to possible thermal overload. Despite parallel connection of a plurality of power sections, therefore, the total nominal power is not available.
Specifically, uneven loading of parallel-connected power sections occurs as a result of varying internal resistances or varying settings of the output voltage regulators. Such variation is always unavoidable owing to component tolerances and/or control unit tolerances if each power section is actuated separately via a dedicated control unit. The power section having the highest output voltage inevitably supplies the most current to the connected load.
In accordance with the prior art, a parallel connection is realized via devices that exhibit a significant output voltage reduction when current increases due to a high resistance. In the case of a parallel connection, the currents at the outputs of the power sections inevitably balance out as a result of this voltage reduction. As soon as one power section delivers a higher power, the output voltage of this power section drops and the other power sections supply more current. This solution is associated with increased power loss due to the high resistance value of the individual power sections.